I tried out the NM State Park annual pass thing a few years ago. Just before I (temporarily) went back to sticks & bricks. I hated it.
There is a reason why that was so cheap: Almost all of their state parks are terrible and worn out. The places with water have almost no water anymore, or the water levels are so low you can now camp on spots that used to be 20-40 feet under water. Even at the original water levels, they would have just looked like a giant hole in the desert that just happens to have water in it. The showers are almost all broken or barely functioning. Many of them have push buttons that you have to push every thirty seconds to keep the warm(ish) water flowing. The trees are all dead, and the tables and stuff are all in disrepair.
One had a scorpion and a giant centipede trapped in a light fixture chasing each other back and forth like some never ending duel to the death. They were there the whole time I was at that park. I got video, but I don't feel like digging it out right now.
Did I go to and survey EVERY campground? Of course not. But I went to a bunch of them. All were equally worn down.
But, the worst part is that the camping isn't really free after you pay the annual fee. You still have to pay a $12 (probably more now) fee to register for each two-week (maximum) stay. So, for a year of camping you have to pay for the annual pass (I forget how much that was) PLUS $12 × 52 ÷ 2 = $312. That more than doubled the cost of camping there. Oh, and if you want to cancel a reservation, they want to charge you a fee that would be about half of what you would have paid if you didn't have the annual pass. So you would end up paying more if you try to cancel. It's insane.
Is it still cheap? Yes. But they make no mention of that, at all, until after you have bought the annual pass and go to reserve a campsite. That's false advertising, in my book. For some poor person who spent their "last dime" on the annual pass, that could be devastating.
Also, a lot of the campgrounds have limited seasons, based on average weather from 20 years ago. So, you will see campgrounds listed as closed for the winter, when the temperature there is now in the 50s. Again, you don't really see that info until you go to reserve a site.